The present invention relates to a liquid cutoff valve unit provided for a fuel tank of, for example, a vehicle, capable of discharging gas such as fuel steam from a discharge passage connected to the cutoff valve unit and preventing liquid such as fuel from leaking outside the discharge passage.
FIG. 7 shows one conventional liquid cutoff valve unit of the kind mentioned above, which is provided for a fuel tank of a vehicle.
Referring to FIG. 7, a liquid cutoff valve unit 102 is mounted to an upper portion of a fuel tank 101 and adapted to flow air and fuel steam G101 in the fuel tank 101 into a canister 104 through a discharge line 103 to thereby liquify the fuel steam G101 and feed it to an intake side of an engine, not shown for preventing the generated fuel steam G101 from causing a counterflow thereof and discharging through an fuel supply port.
The liquid cutoff valve unit 102 is also provided with a function for preventing a fuel L101 from leaking through the discharge line 103 at a time when a liquid level of the fuel L101 in the tank 101 rises when the fuel is supplied or a vehicle body is oscillated or when a vehicle is tilted or rolled.
FIGS. 8A and 8B are sectional views of the cutoff valve unit 102 of FIG. 7 for the explanation of the structure and functions thereof, in which FIG. 8A shows a normal (used) state that the cutoff valve unit 102 does not attain a liquid cutoff function and the fuel steam G101 can be discharged and FIG. 8B shows a state that the liquid cutoff valve unit is closed when a liquid level of the fuel L101 rises, and attains the liquid cutoff function.
In FIGS. 8A and 8B, a float chamber 110a, in which a float 111 is accommodated, is formed in a case member 110. The float 111 floats by a buoyancy (floating force) caused by a force of the fuel L101 flowing into the inside of the float chamber 110a through a communication port 112a formed to a cap 112 mounted to an lower end portion of the case member 110 and then rises upward in the illustrated state.
A valve body 111a in form of annular seal performing a sealing function is disposed to an upper portion of the float 111 and a valve seat 111b corresponding to the valve body 111a is disposed to an upper portion of the float chamber 110a. The float 111 has an approximately cylindrical structure having an upper sealed end (on the side to which the valve body 111a is mounted), and the inner cylindrical portion is formed as an air reservoir 111b to thereby obtain the buoyancy. The valve body 111a and the valve seat 110b constitutes, in combination, a float valve 105. Reference numeral 113 denotes a spring as an urging means for adjusting the buoyancy of the float 111 and the spring 113 always urges the float 111 with a urging force smaller than the self-weight of the float 111 in such a manner that the float is not moved upward and the float valve 105 is not closed at a normally standing attitude as far as any buoyancy is not applied.
The valve seat 119b is formed as one end portion of a cylindrical vent member 110c, which has another one end portion formed as a valve seat portion 110d connected to the discharge line 103 through a diaphragm valve 120 abutting against the valve seat portion 110d. The diaphragm valve 120 is opened by a pressure difference between the inner pressure of the diaphragm valve 120 and the inner pressure of the fuel tank 101, and in order to introduce a pressure corresponding to an atmospheric pressure (or negative pressure), a filler port 106 is provided for a working chamber R101 and the filler port 106 is connected to a filler tube (fuel supply portion) 107 through a filler line 108 as shown in FIG. 7.
In a state that the pressure difference between the inside of the fuel tank 101 and the working chamber R101 is small, the valve seat portion 101b is closed because of the urging force of the spring 121 in the valve closing direction and the valve seat portion 101b is opened at a time when a pressure more than a predetermined pressure difference, for example, at a time of fuel supply, is created, the diaphragm valve 120 is opened to thereby flow out the fuel steam G101 into the discharge line 103.
The diaphragm valve 120 is further provided with an orifice 122 for achieving fine (minute) communication between the working chamber R101 and the inside of the fuel tank and the working chamber R101 so as to discharge the fuel L101, by a little amount, flowing into the working chamber R101, into the fuel tank 101.
In the structure mentioned above, the reason why the working chamber R101 does not take a position released for introducing the atmosphere and takes a position sealed through the connection to the filler tube 107 resides in that the fuel steam G101 passing through the orifice 122 and pressure films of the diaphragm valve 120 can be prevented from being directly discharged into the atmosphere. Such a case as that the fuel steam G101 passes through the pressure film will occurs in a case where the pressure film is formed of a thin film made of a rubber elastic material. Further, the fuel supply port formed to the opened end of the filler tube 107 is generally closed by a cap and the fuel cannot be discharged outward therethrough by the venturi effect of the fuel L101.
Accordingly, in the state of FIG. 8A, the float 111 is positioned downward without receiving any buoyancy of the fuel L101, and when the inner pressure of the fuel tank 101 is increased at a time of, for example, fuel supply, the fuel steam G101 passes the communication port 110e opened to the upper portion of the float chamber 110a and flows into the vent portion 110c through the valve body 111a and the valve seat 110b which are now opened. The fuel steam G101 is then flowed towards the discharge line 103 through the diaphragm valve 120 which has been opened by the pressure difference caused at this time.
On the other hand, in the state of FIG. 8B, the liquid, i.e. fuel, level is increased upward by, for example, fuel supply and the fuel L101 is then flowed into the float chamber 110a. In this instance, the float 111 is moved upward and the float valve 105 is closed to thereby cutoff the communication with the discharge line 103.
Under the state mentioned above, the fuel steam G101 in the fuel tank 101 is also not discharged, and when the fuel is further supplied, the liquid level in the filler tube 107 is increased and the operation of, for example, an fuel supply gun is automatically stopped, thus stopping the fuel supply. When the liquid level L101a in the fuel L101 in the float chamber 101 downs, the float 111 is also moved downward to thereby open the float valve 105 in the state such as shown in FIG. 8A.
In the conventional structure of the liquid cutoff valve unit 102 mentioned above, the buoyancy of the float 111 largely depends on an air reservoir 111b formed inside the float 111. Accordingly, in the state of the fuel tank 101 which has normal standing attitude, the air and the fuel steam G101 are not flowed out from the air reservoir 111b and the buoyancy is hence not largely lowered. However, in a case where a vehicle is largely tilted or rolled over, the air and fuel steam G101 in the air reservoir 111b are flowed out and, hence, the buoyancy of the float 111 will be changed.
FIG. 9 includes views for explaining a roll-over test executed for confirming and evaluating the fact whether the liquid cutoff valve unit 102 can maintain its normal functions even if the buoyancy of the float 111 varies.
In the roll-over test, it is necessary to confirm and evaluate the functions of the liquid cutoff valve unit 102 at the roll-over time of the vehicle with respect to the filling condition of the fuel L101 from approximately fuel empty state to approximately fuel fill-up state in the fuel tank 101. For example, test are performed with respect to the fuel amount in the fuel tank 101 by gradually changing the fuel to the amount of 1/4 (approximately empty state), 1/2, 3/4 and 4/4 (approximately fill-up state), and the respective views of FIG. 9 represent the roll-over tests performed at the time of the fuel fill-up state in the tank 101.
More in detail, FIG. 9A shows a test starting state in which the fuel tank 101 is in a normal standing attitude and the liquid level L101a gives buoyancy to the float 111, which is hence moved upward to thereby close the float valve 105.
FIG. 9B shows a state in which the fuel tank 101 is rotated rightward, as viewed, by 90.degree. about the inner central portion of volume C1 thereof as the rotational axis. In this step, a change of time from the state of FIG. 9A to that of FIG. 9B constitutes one condition for the test, and in this example, it is assumed that it takes three minutes. The state of FIG. 9B is maintained for five minutes.
In a manner similar to that mentioned above, the fuel tank 101 is rolled succeedingly by 90.degree. from the state shown in FIG. 9B to the state shown in FIG. 9C, then from the state shown in FIG. 9C to the state shown in FIG. 9D, and finally, to the state shown in FIG. 9E, which is the same standing state as that shown in FIG. 9A after one rotation of the fuel tank 101. This rotation cycle is repeated by several times in the same direction or reverse direction, and thereafter, fuel leaking amount during such rotation cycles of the fuel tank 101 is measured. According to this manner, the function of the liquid cutoff valve unit 102 is examined and evaluated.
However, in the structure of the float 111 in which the air (including the fuel steam G101) existing in the air reservoir 111b, there may cause a case where the air in the air reservoir 111b is vented (breathed) and, in such case, when the fuel tank 101 is turned from the state shown in FIG. 9A to the states shown in FIGS. 9B and 9C during the first one rotation cycle, the air does not substantially exist in the air reservoir 111b in the state shown in FIG. 9E. In this state, the buoyancy of the float 111 is reduced and the float valve 105 easily takes a valve opened state. From this state, the fuel tank 101 is further rotated, there may cause a case where much fuel leaking through the opened float valve 105 during the rotating process from the state shown in FIG. 9A to the state shown in FIG. 9B is observed and measured by the roll-over tests.
In further conventional art, there has been provided, as a countermeasure to such problem, a liquid cutoff valve unit 202 shown in FIG. 10 having a structure in which the float 111 is formed, at its upper end portion, with a predetermined number of fine communication ports 203, each having a small diameter, for venting the air from the air reservoir 111b for reducing the buoyancy caused by the air in the air reservoir 111b, and the reduced buoyancy is adjusted by increasing a spring constant of the spring 113. The other structural elements of the liquid cutoff valve unit 202 of FIG. 10 other than the above structure are substantially the same as those of the cutoff valve unit 102, the descriptions thereof are omitted herein by adding the same reference numerals in FIG. 10.
According to this structure, however, the valve opened degree, i.e. position, of the float valve 105 is changed in response to the fuel supply speed, and much difference will be caused in the fuel fill-up amount at the fuel supply time. That is, in a case where the fuel supply is performed slowly to gradually increase the liquid level L101a in the fuel tank 101, the air in the air reservoir 111b is discharged through the communication port 203 in accordance with the increasing, i.e. rising, of the liquid level L101a and, hence, when the liquid level reaches a relatively high position, the float valve 105 is closed as shown in the state of FIG. 11A. On the other hand, in a case where the liquid level L101a is rapidly increased, the air in the air reservoir 111b to be discharged through the communication port 203 is temporarily stored therein because the air discharging does not follow up to the rapid increasing of the liquid level L101a, and this stored air acts to the float 111 as buoyancy. A large amount of air, including the fuel steam G101, is discharged through the valve seat portion 110b, which results in the pressure lowering by which a sucking force is applied to the float 111 to easily open the same. Accordingly, in such case, the float valve 105 may be closed at the lower liquid level in the fuel tank 101 as shown in the state of FIG. 11B.
Thus, as mentioned above, when the fuel is rapidly supplied, the float valve 105 is closed faster in time, corresponding to the difference D1 in the liquid surface levels L101a between the states of FIGS. 11a and 11B. Therefore, the float valve 105 is closed at different liquid level in the fuel tank 101 in response to the difference fuel supply speeds, resulting in the difference of the fuel fill-up amount in the tank 101.